HLH is separated into primary HLH (pHLH), caused by germline mutations in immune regulation, classically involving dysfunction in CD8 T cell or NK cells resulting in unchecked activation of macrophages, and secondary HLH (sHLH) characterized by HLH after an initial dysregulating disease such as an autoimmune disorder, EBV infection, malignancy, metabolic disorders, or overwhelming infection [115, 116]. The gene discussed is CD8A; the disease is hemophagocytic syndrome.